Quantum path interference (QPI)

For each harmonic energy within the plateau region there are two main contributing electron trajectories: a short and a long trajectory. The phase associated to each quantum path of harmonic order is given by the classical action along the corresponding trajectory, and can be approximated by the product of the ponderomotive energy with the electron excursion time. The longer the trajectory, the stronger the intensity dependence of the associated dipole phase.
The relative phase between the different trajectories leads to interference in the total single-atom dipole moment and to a fast oscillation of the harmonic emission with increasing intensity. This was experimentally observed for the first time in 2008 here at ETH Zurich.

First experimental observation of QPI: DownloadRef. [269] (PDF, 1.3 MB)

QPI in different gases: DownloadRef. [286] (PDF, 6.2 MB)

Theory of QPI: DownloadRef. [290] (PDF, 6.2 MB)

Spatial finger-print of QPI – more experimental evidence for QPI: DownloadRef. [295] (PDF, 515 KB)